Seismicity, fault rheology, and fault evolution across Africa

Proposal Summary:

This project will investigate the seismicity associated with the major tectonic regimes of Africa using a combination of earthquake seismology, satellite geodesy, and structural geology.  The range of tectonic environments, styles of deformation, and geological settings in which active faulting and seismicity take place provide an ideal opportunity to investigate the controls that rheology of both the fault zone and the bulk lithosphere play on the evolution and interaction of fault systems, and their expression in seismic activity.

Africa hosts a wide variety of deformational regimes, from compression along the margins of North Africa, focussed extension extending from the oceanic rifts of the Red Sea and the Gulf of Aden, through the Afar, to the continental rifts of East Africa, diffuse extension and distributed rifting in southern Africa, and intraplate deformation across the Congo basin and the Okavango.  All of these regimes behave seismically (see Figure 1).  This wide range of tectonic settings spanning the entire continent, presents an opportunity to investigate how variations in the geological context (controlling both the rheology of individual fault zones, and the larger-scale bulk rheology of the lithosphere) influence the seismicity, and the style and evolution of faulting.

This project will initially focus on investigating the seismicity of East Africa, along the rift system, using a combination of earthquake seismology and satellite geodesy.  East Africa shows a well-established first order increase in lithospheric strength from north to south, accompanied by a concomitant increase in the scaling the tectonic structures (Figure 2).  With increasing data coverage (at both global and regional scales, seismologically, along with the advert of short-repeat-time satellite coverage from the ESA’s Sentinel satellites), the project will aim to improve the resolution at which these variations are observed, furthering our understanding of the controls on this process.  The project will then use this revised understanding to address the question of the evolution and interaction of the fault systems along the rift system, drawing on both satellite data and structural geology.

This initial project will train the successful candidate in research, providing a range of technical skills that can then be applied to a whole set of problems relating to the tectonics and seismicity of Africa, based on the students interests.  Avenues exist in East Africa to look at the longer-term dynamics of the faulting process, either on decadal timescales using satellite geodesy, or on Quaternary timescales through the evolution and interaction of fault networks.  As well as widespread seismicity, Eastern Africa also hosts a fascinating interplay between tectonic and magmatic extensional processes, and presents an opportunity to study the interaction and feedback between these two modes of extension – both at the level of individual events, and in terms of the longer-term tectonic evolution of the rift system.

Figure 1:  Seismic Activity of Africa:  After Craig et al., (2011).

Alternatively, the project may evolve to investigate comparisons between the seismicity and faulting associated with extensional in East Africa, and the compressional tectonics of North Africa, with a potentially-lucrative avenue looking at the influence that the tectonic deformation in these two settings has on the longer-term landscale evolution.

The successful candidate will be part of the Tectonics Research group of the Institute of Geophysics and Tectonics (School of Earth and Environment) of the University of Leeds. The Tectonics Research group is a large and dynamic research group including Seismology, Structural Geology, Geomorphology, Quaternary Research and Remote Sensing. The PhD student will benefit from training from the Leeds-York-Hull Doctoral Training Partnership as well as from training at the university, and will be attending national and international conferences and workshops. Possibilities for participation in fieldwork might arise in other projects at the Institute for Geophysics and Tectonics.

Figure 2:  ASTER GDEM topography for four graben systems in East Africa with distinct fault styles.

References:

  • A. Copley et al., (2012).  Constraints on fault and lithosphere rheology from the coseismic slip and postseismic afterslip of the 2006 Mw 7.0 Mozambique earthquake, Journal of Geophysical Research, v117, doi: 10.1029/2011JB008580.
  • T. J. Craig et al., (2011). Earthquake distribution patterns in Africa: Their relationship to variations in lithospheric and geological structure, and their rheological implications, Geophysical Journal International, v185, p403-434.
  • C.J. Ebinger et al., (2019).  Kinematics of Active Deformation in the Malawi Rift and Rungwe Volcanic Province, Africa, Geochemistry, Geophysics, Geosystems, doi:10.1029/2019GC008354.
  • A. Lavayssiere et al., (2019).  Depth extent and kinematics of faulting in the southern Tanganyika Rift, Africa, Tectonics, v38, pp842-862.
  • T. J. Wright et al., (2012).  Geophysical constraints on the dynamics of spreading centres from rifting episodes on land, Nature Geoscience, v5 doi:10.1038/NGEO1428.

 

Objectives:

In the initial phase of this project, you will work to accurately map out the occurrence and style of seismicity associated with the East African Rift System using a combination of earthquake seismology and satellite geodesy, with the aim of understanding how variations in geological structure impact on the distribution of seismicity, and the strength and structure of the associated faults.  Depending on your interests, this will be followed by a combination of  further studies of the seismicity and faulting in the compressional regions of North Africa, investigation of the longer-term processes associated with large-magnitude earthquakes in Africa, studies on the growth and interaction of fault networks in the extensional and transtensional regimes of East Africa, and impact these may have on the landscape, work on the driving factors behind intraplate seismicity across the rest of Africa.  Should relevant large earthquakes occur during the course of the project, you will also be involved in studying the source process and impacts of these events.

 

Fit to NERC Science:

This project constitutes fundamental research into Earth processes and therefore fits well within the remit of NERC science. The project fits into the research areas of Tectonic Processes, Geohazards and Mantle and core processes. The project will have implications for seismic hazard in a range of countries, including several currently on the DAC list, and therefore of UKRI interest under the Global Challenges Research Fund.

 

Applicant Background:

This project would suit candidates with a background in quantitative geology, geophysics, or physics with an interest in solid-Earth processes.  Prior experience in observational seismology or active tectonics is desirable, but not required.

 

Training:

The student will work under the supervision of Dr. Tim Craig and Prof. Tim Wright, within the Institute for Geophysics and Tectonics.  The student will receive training in observational earthquake seismology, satellite remote sensing, and numerical geodynamic modelling.  They will also receive additional training through the Doctoral Training program hosted by the Faculty of Environment and the University of Leeds and the Doctoral Training Partnership.  Within Leeds, they will have the opportunity to interact with internationally-excellent research groups in Tectonics and Geodesy, hosted within the Institute for Geophysics and Tectonics.  The School of Earth and Environment also hosts numerous staff from the NERC-funded Centre for the Observation and Modelling of Earthquakes and Tectonics (www.comet.nerc.ac.uk), with whom the student will be able to interact.